1. Field
The following description relates to optical communication technology, and more particularly, to signal amplification technology.
2. Description of the Related Art
Recently, following the continued increase in data traffic of wired/wireless communication networks, communication service providers are requiring a large-scale transmission system able to accommodate the increased data traffic by expanding insufficient transmission capacity. A large-scale wired optical communication transceiver is essentially required for establishing the transmission system. The optical communication transceiver is required to develop an element with a broader bandwidth for processing a larger amount of data.
A transimpedance pre-amplifier (TIA) is an amplification circuit essentially used in an optical communication system, and is an element that uses low-noise-amplification on a weak signal that converts light into an electric current through a photodetector, such as a photodiode (PD), and transfers the amplified signal as a voltage signal to a subsequent electronic device. A bandwidth that decides an operating speed of the TIA is one of the important design parameters, and generally, a bandwidth of the TIA is designed to be about 70% to 80% of a data speed. This value takes into consideration a noise effect and inter-symbol interference (ISI). The most important parameter that restricts the bandwidth of the TIA is the parasitic capacitance value of an input. Most parasitic capacitances are parasitic capacitances of a PD, a chip pad, an electrostatic discharge circuit, and input transistors. Among such elements, an element with the greatest value is the PD, and has a value of about 300 fF to 1.5 pF.
Above all, a time constant value (τ=RC) of an input is important for increasing a bandwidth. This is because the most dominant pole among the entire optical receiver is decided in an input end of the TIA. For this reason, it is impossible to perform high-speed communication of a higher frequency. Therefore, in order to overcome a large input parasitic capacitance and achieve broadband, an input impedance must be reduced. Since a capacitance of an input end is larger than other portions, by lowering a resistance of the input end, a position of a pole (1/RC) moves to a position of high frequency, thereby increasing bandwidth. Therefore, the TIA circuit's design is required to have small input resistance while obtaining larger gain.